1. Field of the Invention
The invention relates to a hydraulic control arrangement for controlling a number of consumers in accordance with the preamble of claim 1 as well as to a control method for a hydraulic control arrangement of this type.
2. Description of Related Art
Such hydraulic control arrangements are used especially in mobile working machines, for instance wheel loaders or tractors, in order to supply the consumers thereof, for instance the working hydraulics, the steering system or the traveling drives as well as ancillary equipment with hydraulic fluid.
From U.S. Pat. No. 5,540,049 a closed-center system is known in which the hydraulic fluid supply is carried out by means of an electrically controlled variable-displacement pump. A bypass valve by means of which a connection to the tank can be opened is allocated to the variable-displacement pump. The variable-displacement pump, the bypass valve and closed-center valves connected upstream of the consumer are controlled electrically by means of control devices, inter alia in response to the pump pressure and the travel distance of one of the valve slides of the closed-center valves. Thus, in this known solution an electronic velocity or power control of the consumers is performed.
From EP 0 462 589 B1, EP 0 432 266 B2 and DE 41 27 342 C2 hydraulic control arrangements are known which are in the form of a LS system. In such LS systems the pump capacity of the pump is controlled such that a pump pressure lying above the maximum load pressure of the consumers by a defined pressure difference Δp is prevailing in the pump line. In the known systems an adjustable metering orifice and an individual pressure scale by which the hydraulic fluid volume flow to the consumer can be kept constant in response to the adjustment of the metering orifice in a load-independent manner are allocated to each consumer. In said LS systems an input pressure scale by means of which a connection to the tank can be opened can be provided downstream of the pump. A control pressure corresponding to the maximum load pressure is applied to said input pressure scales in the closing direction. The pressure difference at which the input pressure scale opens is usually slightly greater than Δp adjusted by the pump.
For connecting mounted implements or ancillary equipment without an independent hydraulic fluid supply a power-beyond port, as it is called, is provided which may include a pressure line, a return line and a LS line. Said power-beyond port permits the use of the load-sensing system of the working machine also for the mounting implement. Such solutions are known, for instance, from DE 102 14 850 A1 and DE 42 39 109 C1.
It is a problem in hydraulic control arrangements provided with power-beyond ports that no information about the required hydraulic fluid volume flow of the consumer or consumers connected to the power-beyond port (power-beyond consumers) is provided. In the case of a lack of supply in the system an uncontrolled behavior of one or more consumers may occur depending on the load pressure. In this case it is usually not possible to reduce individual consumers of the system in a well-directed manner in order to operate other priority consumers in a desired manner.
Compared to this, the object underlying the invention is to provide a control method and a hydraulic control arrangement in which, when at least one power-beyond consumer is connected to a power-beyond port, a hydraulic fluid supply of all consumers is improved vis-à-vis the known solutions.